Players may respond to Pacification Array’s ability by activating an ability of the target permanent if that ability’s timing permissions allow it. Players may also respond by activating abilities or casting spells whose costs include tapping the target permanent.

2/9/2017

Once a player has activated an ability with in its cost, Pacification Array can’t be used to undo or counter that ability.

2/9/2017

If you want to stop someone from attacking with a creature by using Pacification Array’s ability, you must do so before attackers are declared. You can’t wait until after attackers are declared and then try to use it to make a creature stop attacking. Note that your opponent can’t start declaring attackers without letting you use your Pacification Array.